Ride or Die was originally a biker term meaning if you couldn't ride you'd rather die. It has now changed to mean anyone (wife, boyfriend, best friend), that you will "ride" ANY problems out with them or "die" trying. The "ride" doesn't always have to be a negative either. Obviously if you're this close to someone you want them to enjoy the "ride" (life and all it has to offer with them as well.

Me and my girl have had some stuff thrown our way, but we're stronger than ever. She's my Ride or Die.

Keith and I went skydiving this afternoon! Ride or Die Baby!! (This usage infers the other is your ROD because you two are sharing the excitement of the ride!

when you are willing to do anything for someone you love or someone you really appreciate in your life. the person who you stand by in any problem and vice versa.
the term "ride till the end or die trying"

To stand by your partner no matter what, through the good and the bad, always taking their side even when you believe they are wrong, sticking up for them even over the most minute put-down someone flings their way, being completely protective of them physically, emotionally and spiritually, and sharing everything together as best friends with full trust and loyalty, to the death.

He's my ride-or-die; he has my back and I have his -- 1000% -- and we trust each other implicitly. Ain't nobody gonna be able to come btwn us.

A once-badass declaration of one's dedication to the art, science, and lifestyle of motorcycling, which has sadly been usurped by fucking idiots who also say 'bae', 'fleek', and 'squad goals' but can't tell the difference between 'they're', 'their', and 'there'.

Me, who rides, speaking to my buddies: "Ride or die, bro!" *does a vroom*
Makeup tutorial moron, who doesn't ride, speaking to the Interwebs: "OMG SO LIEK MY RIDE OR DIE MASCARA IS-" at which point I stab my eardrums with a K-bar.